Method of making an electrical aluminum-copper connection



1965 E. s. HOWARTH ETAL 3,201,853

METHOD OF MAKING AN ELECTRICAL ALUMINUM-COPPER CONNECTION Original Filed April 26. 1960 INVENTOHS Elbe/f S. Howarfh 9} United States Patent M This application is a continuation of our copending application, Serial No. 24,801, filed April 26, 1960, and now abandoned.

This invention relates to an improved joint between aluminum and copper, and to the method of producing such joints. More specifically, this invention relates to an improved electrical connector having a copper contact face and analuminum backing member, and a method for making the connector.

In conventional Welding methods, particularly those other than flash welding, the weld interface between aluminum and copper members is brittle and possesses limited mechanical strength. In addition, the connections show greater electrical resistance than either of the parent metals. These undesirable conditions may be somewhat minimized by flash welding the copper and aluminum members. i

Flash-butt welding or flash welding is usually accomplished by arranging the two pieces to be Welded end to end, connecting them to a suitable source of electricity, establishing and maintaining an arc between them which melts the metal in a localized area at the ends of the pieces, then pushing the pieces together to extinguish the arc and produce the welded joint, and subsequently cutting on the current. Flash welding machines used for this purpose generally comprise a fixed die and a movable die, both adapted to clamp the work pieces, mechanism adapted to drive the movable die to bring the Work pieces together, a suitable source of electricity connected to said dies, such as the secondary of a transformer, and an automatic switch actuated by movement of the die for cutting off the current.

However, it is diflicult to produce a satisfactory flash weld between aluminum and copper pieces of relatively large diameter; The reason is that as the diameter or cross-sectional area of the pieces to be joined increases, longer periods of flashing are required so that in bringing the pieces into contact with one another during arcing, excessive spattering and burning away of the metal occurs.

In the production of aluminum by the electrochemical reduction of alumina, aluminum bus bars for supplying electric current to the carbon anodes are supported above the electrolyte cavity of the reduction cell. Copper anode bars, clamped to the bus, support the carbon anodes and carry current to them. However, the natural oxide film formed on an aluminum surface exhibits high electrical resistance, and consequently a mechanical connection be tween aluminum and copper surfaces is electrically inefficient. This is particularly true under the operating conditions for the reduction cell which carry a high current load operated atelevated temperatures. It is recognized that a copper-to-copper disconnect contact surface between the copper anode bar and aluminum bus is electrically superior to a copper-to-aluminum connecting surface. To obviate the need for a substantially more expensive copper bus bar, it is conventional practice to interpose a copper contact strap between the aluminum bus and copper anode bar. According to this procedure, the bus and copper contact surfaces are cleaned as by 3,Ziil,853 Ce Patented Aug. 24, 1965 wire brushing to remove the oxide film and other extraneous matter, and the copper strap is bolted to the bus.

However, a superior metallurgical bond between the copper anode bar and aluminum bus is provided by Welding the copper contact member to the bus. As explained above, a direct weld between the aluminum and copper members is not feasible. Therefore, it is customary in a connection of this type to provide an interlayer of filler metal compatible with both the aluminum and copper. A silver interlayer, or alloy thereof, is normally employed for this purpose. The copper member is provided with a silver coating as by brazing, and the, coated member is thereafter connected to the aluminum bus by Welding, preferably by inert gas shielded tungsten arc welding. This procedure is obviously disadvantageous in that it not only employs an expensive filler metal but further requires the additional brazing operation. Moreover, the welding operation requires a high degree of skill to avoid burning off the silver interlayer and consequently" impairing the electrical connection. In this regard, tungsten arc welding is easier to control, but is more expensive and time consuming than other conventional metal arc welding procedures.

An aluminum backing may be flash welded to the copper contact member, and from this composite, the aluminum backing may thereafter be joined to the aluminum bus bar. However, it is desirable, as in an aluminum reduction cell, that the electrical contact be capable of carrying a sufficiently high quantity of current and further dissipate the heat generated at a relatively rapid rate. This is realized by employing a contact of sufficiently large diameter or cross-sectional area. However, flash welded electrical contacts of relatively large diameter would entail a substantial capital investment in that the conventional flash Welding machine is not equipped to handle large pieces. Moreover, a machine to handle large pieces requires a greater consumption of electrical power, and further a high percentage of metal is burned off or consumed in the welding operation. That is, for example, joining members of 2 inches diameter would require approximately 4 times the power requirements as members of 1 inch diameter. Further, the time required for flashing would be doubled, and the volume of metal lost-with the larger parts is about 8 times that of the smaller parts. In view of these shortcomings and disadvantages, the contact surface area of flash welded alumimum-copper connectors is restricted, and therefore anum: ber of such connectors must be attached to the bus at the zone of contact with each anode bar. I

This invention has therefore as one of its primary objects to provide a new and improved copper to aluminum joint and method for making the same.

It is anotherobject of the invention to provide a joint of the above type characterized by high electrical conductivity and high mechanical strength.

It is still another object of the invention to provide in a method for making a joint of theabove type which combines a flash welding operation with an upsetting operation.- I

It is a further object to provide an aluminum-copper electrical contact composite having a relatively large surface contact area, and made by a rapid and convenient method.

It is yet a further object to provide an aluminumcopper composite for electrical connection between an aluminum bus bar and a copper anode bar.

These together with other objects and advantages of the present invention will best be understood by referring to the following detailed specification and preferred an aluminumpart which greater in length than the degree of renc asernent of thegcopper part by thealuniinum depends primarily uponlsuch factors as thefcom-pos 'tionof} the metal parts, th t members and the forging techniqu-e' '-emp1oyed,and theY both members should e 3 Y embodiments thereof, and the accompanying In the drawing: a r r t; 7

FIGURE '1 is a perspective view of an aluminumcopper composite formed on-fiashwelding. 7 FIGURE 2is a sectional elevation through a composite such as shown'in FIGURE 1 after upsetting} FIGURE 3 is a view similar to that 'of FIGURE} showing the upset composite weldeddi'rectly to analirminum bus barix r. 7 i

'According to thepresent and anflaluminum member are "flash welded to effect a bond between the abutting ends. The resulting Com drawing. G

invention, a copper member posite is thereaftertcompressed axiallyto upset'the com positethereby -r'esu lting'in-a lateral expansion; Preferably, we employ a relatively 'duc'tilealumi'num member which will expandr'upon compression-to a greater extent than the. copper memberand-therefore'at least partially peripherally'encase thelatter. The metallurgically bonded! i and upset composite having-a"-substantially" increased' copper contact. area backed by the aluminum member 1 may then be welded directlyfto an aluminum bus bar,"

Switchblade or similar electrical conductorfby convert-xi i; tionalmeans. .An aluminum filler metal is employed to; form a weld fillet between' the, conductor andthe' a1umi-- f num backing member; a -2 Referring now more par ticularly tojthe drawings, the} composite, indic'ated generaIlyat '10, is; formed from an);

aluminum member 12 and copper; member 14, preferably' baror rodshapeof substantially eircular'or square CI'CSS', section, and preferably of 99% "purity or better. To effect-the weld, the 'members are"clamped injthe} dies of any suitable flash weldingmachine -(-not=sho'wn,)' with" Lil) the endso'f the members brought together. A weldi'ng, current is passed throughthe parts to bring their'endsfto a- Welding-teniperatu re, and at the same timeipu'shingi 3 theends together to eflt'ectaniintimate'welding bondr be-j tween the members, asillustrated in FIGURE'ZI. It; 7; should beunderstood th'att-he dimensions and particular form of thealuminum andcopper members employed may bevaried, and is somewhat dependent upon the duc- 4 tility of the metal parts, and the desired configuration l ofthe final product, "as willbemore apparent hereafte e; 1 a The resultingaluminum-copper composite lllis forged," or otherwise compressed axially,- in a direction sub'stan-i tially normal to the weld interface {'16 to'reduces'ubstan-E I tially the length at; the composite.---In forging, af'conventional airor steam'hammer, hydraulic press, mechanical press, and the like, may be employed. Assa result of the forging, the'jcornposite;expands laterally toefi'ct f, an'increaseincross-section, having the characteristics il setting,- outward expan'sion'jof the" aluminum member f 12wil1 be greater thereby res'ultjing inatlleast partial peripheral encasement; of the copperpart 14,- as shown in: FIGURE 21 To assure 'properjencasement offthe; I V

phase and eflfect t substantial lateralexpansion of the said copper member," it is -advantageous t'o employ members. of substantially identical crosssection,- andypreferably'.

copper "partbf However, "appropriated imensioningefan proper conditions may the determined by eaperirrienta tion by one skilled in the art} In addition, it maybe ofbenefit in obtainingafdesired shape to heat thejcom posite tolfor ging temperatures -prior to'the compressing} step,.,, Although it ,-is desirable that the. aluminum meme: 7 her be more ductileflin relation to the copper member, 7 I

A xhibit sufi icientiplasticity.jasznot to fracture upon forging The upset composite, shown in- FIGURE 2,1e'xhibits I I a substantialincrease inexposed surface;areaQorc ntact 1 5 .purities, andgaliloys thereofpn a i f r area, :of the'copper member. a result, the composite,

t when employed in 'an'electrical circuit, can carry a greater 'Vquantity of current and dissipate heat at a faster 4 rate than acomposite that has not been upset. This is particularly advantageous in electrical connections carrying high current loads such as those employed in electrolytic cells for theproduction of aluminum. While ;the aluminum-copper weld interface islsomewhat brittle, the pressure w eld eifect obtained onfforging thins out or distributesfthis brittleiphas'e therebyimprovingthe overallajoint which is, particularly advantageous when employing the jo'i'nt under stress conditions.

Our'invention' --is villustrated by the following example wherein a copper red one inch in length of 99.9 purity and an aluminum rod l' A'inches in length of 99% purity, and each with 1% inc'hes diameter, were i joined v at their abutting ends by fiashweldin g. The welded specimen was "compressed axially "to /s 'j ir1ch thickness bymeans'of a Chambersburg,air hammer having 1 /2: tonscapacityf The copper component. expanded laterally to l /e,rinchesxdiameter and ,was completely hacked and surrounded attheperiphery by the aluminum component shavinga diameter of 3 inchesl' This connector has a copper contact surface of. 3.8"ti-mesi the original surface. The

aalurninumencasement permits welding of the connector .by conventional means to -an{ aluminum bus. Referring toFIGURE 3;, an aluminum fillet weld 181is' employedto 'weld directly the connector to aluminum bus bar'20. A copper anode ibar' (not shown) .foriexample, may be con nected :tojtheicopper -fcontact surface of the composite thereby:v effecting "a copper-to copper disconnect. Where desirable, the fiat surface of the aluminum hacking member' offthe'composite may be positioned. over a hole or opening in the conductor or bus and a fillet weldapplied from the'reyerse sidebetween the conductor and backing r member. I

'In additionlto employing the compositela's a connector in' electrolytic reduction cells, it will be apparent thatthe composite may be used in numerous electrical devices where a.copper-to copper rcormection is important, For. example, itis possible to use aluminum switch blades to whichthe' composite hasbeen welded;

As used herein and in the-appended claims the mercial grades of the metalsl c ont'ainin'g the usual in!- 11A method ofirnjalcing a joint betvveen an aluminum 7 and lajcopper meinber, 's aid' aluminumfmember being lustratedin FIGURE 2'. "It is preferred that the alulmi num member employed'in the; composite be- 'relatively" more ductile than the copper part s'uchthat iuponupmore' ductile thanj said copper member, comprising arranging the members IO be joined in 'end t'o-end abutting Qrelation, forming a flash welded'jointbetween the abutting ends of-saidirriembers; saidvj ointhaving a'brittl'e phase at ,:theflash 'weld interface, arid-applying suflicient pressure to the resultant composite in a direction substantially normal to the flash weld interface to, thin out said brittle members; in, directions parallel to the weld interface with upsetting of'said aluminurn-member over said copper member to produce atleast partial peripheral encase "1 ment of s'ai -eopper member by "sa-idupset aluminum zgn a-methiodiof maki'n 'gan electrical connection be-:

tween:an- -aluminumbus I barand a opper anode. bar of an. electrolyticlredu'ction, cell; arranging a 'copper. contact efiect substantial lateraljergpaasion of. the said members o wordsaluminum and. copper include the pure metals, corn- 5 in directions parallel to the Weld interface With upsetting of said aluminum member over said copper member to produce at least partial peripheral encasement of said copper member by said upset aluminum member, and welding said backing member to said bus bar.

References Cited by the Examiner UNITED STATES PATENTS 2,624,820 1/53 Payette 29-15555 6 2,739,369 3/56 Cooney 29497.5 X 2,854,074 9/58 Frank et a1. 200166 OTHER REFERENCES Resistance Welding, first edition, by Wallace A. Stan- 5 18y, published by McGraw-Hill (Welding Dissimilar Metals, page 156, cols. 1 and 2).

JOHN F. CAMPBELL, Primary Examiner. 

2. IN A METHOD OF MAKING AN ELECTRICAL CONNECTION BETWEEN AN ALUMINUM BUS BAR AND A COPPER ANODE BAR OF AN ELECTROLYTIC REDUCTION CELL, ARRANGING A COPPER CONTACT MEMBER AND AN ALUMINUM BACKING MEMBER IN END-TOEND ABUTTING RELATION, SAID ALUMINUM BACKING MEMBER BEING MORE DUCTILE THAN SAID COPPER CONTACT MEMBER, FORMING A FLASH WELDED JOINT BETWEEN THE ABUTTING ENDS OF SAID MEMBERS, SAID JOINT HAVING A BRITTLE PHASE AT THE FLASH WELD INTERFACE, AND APPLYING SUFFICIENT PRESSSURE TO THE RESULTTANT COMPOSITE IN A DIRECTION SUBSTANTIALLY NORMAL TO THE FLASH WELD INTERFACE TO THIN OUT SAID BRITTLE PHASE AND EFFECT SUBSTANTIAL LATERAL EXPANSION OF THE SAID MEMBERS IN DIRECTIONS PARALEL TO THE WELD INTERFACE WITH UPSETTING OF SAID ALUMINUM MEMBER OVER SAID COPPER MEMBER TO PRODUCE AT LEAST PARTIAL PERIPHERAL ENCASEMENT OF SAID COPPER MEMBER BY SAID UPSET ALUMINUM MEMBER, AND WELDING SAID BACKING MEMBER TO SAID BUS BAR. 